Hemiprotosuchus: closer to Aetosaurus than Protosuchus

Not much written about this genus
According to Wikipedia,Hemiprotosuchus is an extinct genus of protosuchid from the Late Triassic (Norian stage) Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina, South America.” 

Figure 1. Hemiprotosuchus leali skull from Desojo and Ezcurra, nests with Decuriasuchus in the LRT. The variation within this clade is increased with this nesting.

Figure 1. Hemiprotosuchus leali skull from Desojo and Ezcurra, nests with Decuriasuchus in the LRT. The variation within this clade is increased with this nesting.

The specimen
(Fig. 1, image from Desojo and Ezcurra 2016) seems to be preserved as a half skull, nearly complete. Bonaparte 1969 first considered this a protosuchid like Protosuchus (Fig. 2), likely due to its low triangular rostrum and high temporal region.

Figure 2. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

Figure 2. Protosuchus skull. The high cranium and low triangular rostrum evidently made Bonaparte 1969 consider Hemiprotosuchus similar enough to Protosuchus.

After testing
in the large reptile tree (LRT, 1594 taxa) Hemiprotosuchus (PVL 3829, Bonaparte 1969; Norian, Late Triassic) nested between Ticinosuchus (Fig. 3) and aetosaurs, like Stagonolepis and Aetosaurus (Fig. 3).  That’s a long way from Protosuchus in the LRT.

In 1969 no one knew
that Ticinosuchus was basal to aetosaurs. The LRT recovered that relationship here in 2011.

Figure 3. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Figure 3. Hemiprotosuhus image from Desojo and Ezccura 2016. Colors added. This taxon is derived from Ticinosuchus, basal to aetosaurs.

Others (e.g. Nesbitt 2011 and works based on that cladogram)
considered Revueltosaurus (Fig. 3) a basal aetosaur. The LRT nests Revueltosaurus closer to the genesis of the Euarchosauriformes (between Euparkeria and Erythrosuchus among lesser known taxa).

Desojo and Ezcurra 2016
accepted the protorosuchian affinities of Hemiprotosuchus without further comment.


References
Bonaparte JF 1969. Dos nuevas ‘faunas’ de reptiles triasicos de Argentina. Gondwana Stratigraphy (IUGS Symposium, Buenos Aires)2:283–306.
Desojo JB and Ezcurra MD 2016. Triassic pseudosuchian archosaurs of South America. Historia Evolutiva y Paleobiogeográfica de los Vertebratos de América del Sur. XXX Jornados Argentinas de Paleontología de Vertebrados. Contribuciones del MACN No. 6: 57–66.

wiki/Hemiprotosuchus

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